using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Immutable;
using System.Linq;
using System.Reflection;
using System.Runtime.Serialization;
using System.Xml;

namespace ser;


// --- Primitive Handler ---
public partial class PrimitiveHandler : ser.ITypeHandler
{
	public object? ReadXml( XmlSer xml, XmlElement elem, Type expectedType, object? existing )
	{
		string val = elem.HasAttribute( "v" ) ? elem.GetAttribute( "v" ) : elem.InnerText;
		if( val == "null" )
			return null;

		// So this is an interesting one. Why not use the expected type? Well, we know we have
		// data in the XML, it just wont convert to what we want.
		return xml._resolver.ConvertSimple( val, expectedType );
	}
}

// --- Proxy Handler ---
public partial class ProxyHandler : ITypeHandler
{
	public object? ReadXml( XmlSer xml, XmlElement elem, Type expectedType, object? existing )
	{
		var ti = xml._meta.Get( expectedType ); // Re-get to ensure we have proxy info
		if( !elem.HasAttribute( "proxy" ) || !ti.ProxyDef.HasValue )
		{
			log.warn( $"Proxy read failed for {expectedType.Name}. Fallback needed." );
			return null; // Should fall back or throw
		}
		var proxyVal = elem.GetAttribute( "proxy" );
		return ti.ProxyDef.Value.fnDes( expectedType.FullName, proxyVal );
	}
}

// --- ISerializable Handler ---
public partial class ISerializableHandler : ITypeHandler
{
	public object? ReadXml( XmlSer xml, XmlElement elem, Type expectedType, object? existing )
	{
		// Create/Get instance (needs FormatterServices for ISerializable)
		object obj = existing ?? FormatterServices.GetUninitializedObject( expectedType );
		long id = xml.TrackIfGraph( obj, elem ); // Track it

		var serInfo = new SerializationInfo( expectedType, new FormatterConverter() );

		foreach( XmlNode objNode in elem.ChildNodes )
		{
			if( objNode is XmlElement childElem )
			{
				string childName = childElem.Name;
				Type? childType = xml._resolver.FindType( childElem.GetAttribute( "_.t" ) );
				if( childType != null )
				{
					var desValue = xml.ReadNode( childElem, childType, null );
					serInfo.AddValue( childName, desValue, childType );
				}
			}
		}

		var context = new StreamingContext( StreamingContextStates.All ); // Or use xml.Context
		var cons = expectedType.GetConstructor(
				BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
				null, new[] { typeof( SerializationInfo ), typeof( StreamingContext ) }, null );

		if( cons != null )
		{
			cons.Invoke( obj, new object[] { serInfo, context } );
		}
		else
		{
			log.error( $"ISerializable type {expectedType.Name} lacks the required constructor." );
		}

		if( obj is IDeserializationCallback cb )
			cb.OnDeserialization( obj );

		return obj;
	}
}

// --- Collection Handler ---
public partial class CollectionHandler : ITypeHandler
{

	public object? ReadXml( XmlSer xml, XmlElement elem, Type expectedType, object? existing )
	{
		// Determine element type
		Type elemType = GetElementType( expectedType );

		// Create a temporary list
		var listType = typeof( List<> ).MakeGenericType( elemType );
		var list = (IList)Activator.CreateInstance( listType )!;

		xml.TrackIfGraph( list, elem ); // Track list if graph

		// Populate the list
		foreach( XmlNode node in elem.ChildNodes )
		{
			if( node is XmlElement childElem )
			{
				list.Add( xml.ReadNode( childElem, elemType, null ) );
			}
		}

		// Convert to the final expected type (Array, Immutable*, List)
		return ConvertToFinalCollection( list, expectedType, elemType );
	}
}


// --- Object Handler (Default/Complex) ---
public partial class ObjectHandler : ITypeHandler
{
	public object? ReadXml( XmlSer xml, XmlElement elem, Type expectedType, object? existing )
	{
		var actualType = xml._resolver.Resolve( elem, expectedType );
		var ti = xml._meta.Get( actualType );

		// 1. Get/Create Instance
		var (obj, _) = GetOrCreateInstance( xml, elem, actualType, existing );
		if( obj == null )
			return null;

		// Handle graph refs (if already processed)
		if( xml._cfg.Structure == Datastructure.Graph && elem.HasAttribute( "ref" ) )
		{
			long id = long.Parse( elem.GetAttribute( "ref" ) );
			if( xml._processed.TryGetValue( id, out var processedObj ) )
				return processedObj;
		}

		// Track if it's new
		xml.TrackIfGraph( obj, elem );

		// 2. Hydrate
		foreach( var memberMeta in ti.Members )
		{



			{
			var (valueSource, isAttribute) = FindValueSource( elem, memberMeta.XmlName );

			if( valueSource != null )
			{
				object? memberValue;
				object? currentMemberValue = memberMeta.GetValue( obj );

				if( isAttribute )
				{
					memberValue = xml._resolver.ConvertSimple( valueSource.Value!, memberMeta.Type );
				}
				else // Child Element
				{
					memberValue = xml.ReadNode( (XmlElement)valueSource, memberMeta.Type, currentMemberValue );
				}

				// Set value, respecting ser.Do/ser.Dont and pre-hydration
				if( ShouldSetValue( memberMeta, existing != null ) )
				{
					memberMeta.SetValue( obj, memberValue );
				}
			}
			}
		}

		// 3. Post-processing
		if( obj is ser.I_Serialize iSer )
			obj = iSer.OnDeserialize( null );
		if( ti.IsImm && obj is imm.Obj immObj )
			return immObj.Record( $"From XML {elem.Name}" );

		return obj;
	}
}